Actually, despite its, uh, antiquity, I like this idea. Let me explain.
1) Why does everyone think that they'll have trouble from blogs for republishing? It's huge extra exposure - I feel that you'll get tons of people interested.
2) Go away from publishing blog posts to stories about the bloggers (egos), about how they started their idea, features on getting started, new stories by bloggers, etc. The TOPIC is blogging, not the posts that they've written. Remember that and you have your focus.
3) It's simply not a topic covered by any major magazine
The bad -
1) Magazines are indeed dying. Ad revenues are down and continue to drop.
2) It's ironic to cover such a new media with such an old one and the irony will hit people as they read it.
3) You're going to need a good deal of money to start this up and do circulation.